The overall objective of the proposed research is the identification of genes of Rous sarcoma virus (RSV), a representative RNA tumor virus, responsible for the initiation and maintenance of the transformed state. The functions specified by such genes, as well as replication functions, will be analyzed by the use of conditional-lethal mutants. In addition, emphasis will be placed on determining the role of membrane alterations in the maintenance of transformation. Such studies will include both physiological and biochemical analyses of the phenotypic alterations of the plasma membrane of transformed cells compared with the parental untransformed cells. Efforts are being continued to study the possible role of plasminogen activator in the maintenance of the transformed state.